Same issue here, trying to use Cubasis with ZED 10FX.
Cubasis 1.9 (latest version on app store)
Apple iPad Air MD788LL/A 16GB Wi-Fi
iOS 8.1 (12B410)
Apple Lightning to USB Camera Adapter
Allen & Heath ZED 10FX
GarageBand is able to record sound and playback over USB using the ZED 10FX, though sometimes it freezes and I need to unplug and replug the USB adapter to get it responsive again. But it is definitely able to communicate with the 10FX.
Cubasis works fine without the 10FX plugged in, but as soon as I plug it in the playback goes quiet. I am also unable to record any sound from it.
Cubasis is enabled in Settings/Privacy -> Microphone, and works fine with the builtin microphone.
Inspector routing settings show stereo input 1+2 and stereo output 1/2, both are enabled but I can’t hear anything on the 10FX or get any sound through to Cubasis from it. Under Setup -> Audio, Input Gain shows “No device” when the 10FX is connected, but goes back to a slider when I disconnect it.
Any help you could provide would be welcome, Cubasis looks pretty neat but is a nonstarter if I can’t get any sound to it.